1. Field of the Invention
The present invention relates to methods for delivering bioactive agents, in particular to methods for delivering bioactive agents to specific regions of the body of a patient.
2. Background of the Invention
Treatment modalities for certain diseases often rely on the ability to target bioactive agents to a diseased region or tissue in the body of a patient, while minimizing or preventing action of the bioactive agents on other regions or tissues in the body, such as undiseased regions or tissues. Examples of bioactive agents which may be targeted to specific regions of the body of a patient include pharmaceutical and diagnostic agents.
Current methods for targeted delivery of bioactive agents are reviewed, for example, in Cronstein and Weissman, "Targets for Anti-inflammatory Drugs", Ann. Rev. Pharmacol. Toxicol. 35:449-62 (1995). One method involves the use of liposomes as delivery vehicles, in which the lipid moiety of the liposome undergoes a phase transition at about 42.degree. C. External heat is applied to produce the necessary temperature increase to induce the phase transition. Specific applications of the use of liposomes for targeted delivery of bioactive agents include treatment of disorders of the eye (see, e.g., Khoobehi, et al., Jpn. J. Ophthamol. 33:405-412 (1989)), and treatment of tumors (see, e.g., Maekawa et al., Cancer Treatment Reports 71:1053-59 (1987)). However, as discussed in Magin et al., Cancer Drug Delivery 3:223-37 (1986), the use of liposomes for targeted drug delivery is limited by the inability of the liposomes to clear the reticuloendothelial system. A further limitation of the method is the necessity of applying external heat to obtain a temperature of 42.degree. C. or higher.
Structural features, such as tumor antigens, are also used in targeting delivery of a bioactive agent to a particular region or tissue. However, such structural features are associated with one or, at most a few, disease states. In addition, incomplete or irregular expression of such structural features may further limit their usefulness in targeted delivery of bioactive agents.
Accordingly, a need continues for new and/or improved methods for targeting specific regions or tissues in the body of a patient, and delivering bioactive agents to the targeted regions or tissues. The present invention is directed to these, as well as other, important ends.